Along with an increase in output power and efficiency of a light-emitting diode (LED), the LED is capable of outputting luminous flux similar to that of a fluorescent lamp. With a wide spread use of such an LED, a luminaire such as an LED base light and an LED down light having an LED as a light source is developed.
An LED as a light source has a feature of a long life as compared with other light sources based on the technologies to date. This is advantageous in the maintenance, because the frequency of replacing the light sources or the luminaires are reduced. Further, a single piece of LED is compact and therefore has a high degree of freedom in optical design. With a development of a further efficient LED, a luminaire of a type different from the conventional one will be developed.
In the meantime, the LED is affected by heat generated while being lit, which causes a decrease in luminous flux, light-emitting efficiency, or a life of the LED. For this reason, it is necessary to design the light-emitting module or the luminaire having the LED as a light source by considering how to dissipate the heat generated by the LED. Therefore, the luminaire that utilizes the LED as a light source is subject to a structural restriction or the like, despite the fact that a single LED itself is compact and light.
A luminaire using an LED as a light source is described in Jpn. Pat. Appln. KOKAI Publication No. 2004-253478. This luminaire includes a substrate on which a plurality of LEDs are arranged and a reflecting plate provided with reflection surfaces that individually surround the LEDs. Such a luminaire, in general, should have a structure in which heat is radiated from a rear side opposite to an illumination side. For example, a luminaire of a ceiling-embedded type has a structure in which heat is radiated from a rear side thereof toward the ceiling cavity. A luminaire of a ceiling-mounted type is provided with a gap through which air flows between a ceiling surface and a rear surface of the luminaire.